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Phy107Spr06Lect22 - Title paragraph example Course Essay T...

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1 Mar. 20, 2006 Phy107 Lecture 22 1 Course Essay 500-750 word typed essay due Wed. Apr. 26 First deadline: Fri. this week (Mar. 24) turn in Topic and Paragraph Description Topic ideas: Nobel prize winner: work & importance Big science project: mission & successes Bogus or contentious science: any scientific support? Science topic: achievements and outlook See course web site for details and resources Mar. 20, 2006 Phy107 Lecture 22 2 Title / paragraph example Topic: Quantum Computers Paragraph: Over the last decade, scientists have developed new approaches to computing using basic ideas of quantum mechanics. Individual atomic particles are used as ‘bits’ of a computer, but instead of representing only ‘0’ and ‘1’, the quantum-mechanical wavefunction is used to simultaneously represent an infinitely variable range of values. Such systems have the potential to revolutionize computing, but only for specialized problems such as factoring large numbers. The scientific aspect I will discuss is the use of trapped atoms as quantum bits. I will also discuss the background and operating principles of quantum computers, and the potential achievements of quantum computers. Description of topic Outlook What else I will write Science aspect Mar. 20, 2006 Phy107 Lecture 22 3 From Last Time… Light shows both particle and wavelike properties Interference is an example of wavelike props. Photons are particles of light in the particle-like description. An Experiments demonstrating this was Photoelectric effect Einstein received Nobel prize for his explanation of the photoelectric effect. Mar. 20, 2006 Phy107 Lecture 22 4 Photoelectric effect summary Light is made up of photons, individual ‘particles’, each with energy hf One photon collides with one electron - knocks it out of metal. If photon doesn’t have enough energy, cannot knock electron out. Intensity ( = # photons / sec) doesn’t change this. Minimum frequency (maximum wavelength) required to eject electron = hc " = 1240 eV # nm " Mar. 20, 2006 Phy107 Lecture 22 5 Photoelectric effect question An electron is bound inside copper by a ‘binding energy’ of 4 eV. Which wavelength will eject electrons from copper? A. 300 nm B. 500 nm C. 700 nm Minimum photon energy to eject electron is 4 eV. Corresponding photon energy is given by So λ max =310 nm 4.0 eV = hc " = 1240 eV # nm " nm Mar. 20, 2006 Phy107 Lecture 22 6 Compton scattering Collision of photon and electron in vacuum Photon loses energy, transfers it to electron Photon loses momentum transfers it to electron Total energy and momentum conserved Before collision After collision Photon energy E = hf Photon mass = 0 Photon momentum p = E / c
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2 Mar. 20, 2006 Phy107 Lecture 22 7 Compton scattering Photons can transfer energy to beam of electrons.
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